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Examples_target_update.tex
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Examples_target_update.tex
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\pagebreak
\chapter{\code{target} \code{update} Construct}
\label{chap:target_update}
\section{Simple \code{target} \code{data} and \code{target} \code{update} Constructs}
The following example shows how the \code{target} \code{update} construct updates
variables in a device data environment.
The \code{target} \code{data} construct maps array sections \plc{v1[:N]} and \plc{v2[:N]}
(arrays \plc{v1} and \plc{v2} in the Fortran code) into a device data environment.
The task executing on the host device encounters the first \code{target} region
and waits for the completion of the region.
After the execution of the first \code{target} region, the task executing on
the host device then assigns new values to \plc{v1[:N]} and \plc{v2[:N]} (\plc{v1} and \plc{v2} arrays
in Fortran code) in the task's data environment by calling the function \code{init\_again()}.
The \code{target} \code{update} construct assigns the new values of \plc{v1} and
\plc{v2} from the task's data environment to the corresponding mapped array sections
in the device data environment of the \code{target} \code{data} construct.
The task executing on the host device then encounters the second \code{target}
region and waits for the completion of the region.
The second \code{target} region uses the updated values of \plc{v1[:N]} and \plc{v2[:N]}.
\cexample{target_update}{1c}
\fexample{target_update}{1f}
\section{\code{target} \code{update} Construct with \code{if} Clause}
The following example shows how the \code{target} \code{update} construct updates
variables in a device data environment.
The \code{target} \code{data} construct maps array sections \plc{v1[:N]} and \plc{v2[:N]}
(arrays \plc{v1} and \plc{v2} in the Fortran code) into a device data environment. In between
the two \code{target} regions, the task executing on the host device conditionally
assigns new values to \plc{v1} and \plc{v2} in the task's data environment. The function \code{maybe\_init\_again()}
returns \plc{true} if new data is written.
When the conditional expression (the return value of \code{maybe\_init\_again()}) in the
\code{if} clause is \plc{true}, the \code{target} \code{update} construct
assigns the new values of \plc{v1} and \plc{v2} from the task's data environment to the corresponding
mapped array sections in the \code{target} \code{data} construct's device data
environment.
\cexample{target_update}{2c}
\fexample{target_update}{2f}